(1) Field of the Invention
The present invention relates to a projection-type display apparatus enlarging and projecting an optical image formed on a display device such as a liquid crystal display and a multiscreen display apparatus using the same.
(2) Description of the Related Art
A conventional projection-type display apparatus generally uses a lamp as a light source, and the brightness is high in the initial stage of use but decreases over the time of use. There are known related arts to compensate the loss of brightness as described, for instance, in Japanese Patent Laid-open No. 2-73241 (document 1) and Japanese Patent Laid-open No. 2001-117164 (document 2).
Document 1 discloses a technique for controlling the brightness so as to be stable on a screen by providing a light detector (hereinafter referred to as “detector”) for detecting the brightness (light intensity) in proximity to the screen of the projection-type display apparatus, and by adjusting an amount of input power to be supplied to the light source based on the output of the detection. Document 2 discloses another technique by disposing the detector in the middle of the light path from the light source to the display device. Document 2 further discloses a technique for controlling the brightness so as to be stable on a screen by adjusting an amount of input power to be supplied to the light source based on the output of the detection, as disclosed in document 1.